Presently, a soliton pulse generated by optical fiber laser is desirable in the area of high-speed optical communication since it has a short pulse width. A conventional passive mode-locked optical fiber laser requires an increased output of a pump source to generate a soliton pulse and the generated pulse is oscillated as a form of bunch. Therefore, in order to generate a soliton optical short pulse, the output of the pump source needs to be down to threshold current.
Previous studies have been conducted by D. I. Laming, D. N. Payne, V. J. Matsas, M. W. Philips in April and August, 1991.
The title of the technical paper published in April 1991 is "320 fs soliton generation with passively mode locked erbium fiber laser", IEEE Electronics Letters, Vol. 27, No. 9, pp. 730.about.732. The title of the technical paper published in August 1991 is "Pulse repetition rates in passive, selfstarting, femtosecond soliton fiber laser", IEEE Electronics Letters, Vol. 27, No. 16, pp. 1451.about.1453.
According to these previous studies, optical fiber lasers autonomously generate a pulse by increasing pump output and a multiple soliton optical pulse is generated within a period. When pump output is decreased slowly in the state, the number of multiple soliton optical pulses is decreased. When the pump current gets close to the threshold current, one soliton optical pulse is generated within a period.
However, when the pump current gets decreased close to the threshold current, the output of the soliton optical short pulse generated by the optical fiber laser may have a seriously low value and therefore efficiency of the pump output is lowered.